1. Field of the Invention
The present invention relates to a semiconductor device resin-encapsulated with a cured resin piece having adequate electric insulation properties and an electromagnetic wave shielding function, and an epoxy resin composition used for encapsulating a semiconductor in the semiconductor device.
2. Description of the Related Art
Generally, the problem of EMC (Electro-Magnetic Compatibility) has been obvious in electric equipment. Measures against the problem have been taken from the two perspectives: emission of unnecessary electromagnetic waves and durability. In recent years, with the advance of miniaturization and higher functions of information communication equipment, semiconductor elements have a tendency to further increase their operating frequencies in order to have higher performance. Particularly with digital signals processed at a higher rate, amplitude values of the signals become lower in order to reduce power consumption. Thus, there is increasing a risk that even weak radio-frequency noise causes a malfunction.
Covering of a semiconductor package with a metal cap has been heretofore carried out as one measure against this risk. However, since an extra mounting space is required, the mounting density of electronic parts cannot increase satisfactorily. Accordingly, other solutions have been under investigation. Nowadays, from such a background, an electromagnetic wave shielding technique suitable for high-density mounting is demanded. If an epoxy resin composition itself used as a encapsulating material has an electromagnetic wave shielding function, electronic parts can be mounted at a high density. Therefore, investigations have been made chiefly into the addition of the electromagnetic wave shielding function to the epoxy resin composition. However, any related-art cured piece made of an epoxy resin composition in which inorganic filler chiefly composed of silica powder has been mixed and dispersed has no electromagnetic wave shielding function at all.
From such a point of view, for example, as a technique for adding an electromagnetic wave shielding function directly to an encapsulating resin material for encapsulating a semiconductor element, a resin-encapsulated semiconductor device having a double-layer structure of encapsulating resin layers has been proposed as disclosed in Unexamined Japanese Patent Publication Hei. 3-23654. One of the encapsulating resin layers is a encapsulating resin layer in which the outside portion of a semiconductor package is encapsulated with resin in which ferromagnetic particles has been dispersed, and the other is an encapsulating resin layer in which the inside portion of the semiconductor package is encapsulated with related-art insulating encapsulating resin. Thus, there is disclosed a technique which can prevent malfunction of a semiconductor element from occurring due to electromagnetic noise. However, some resin in which ferrite or the like has been mixed and dispersed is often inferior in electric insulation properties due to its insufficient specific resistance. Thus, there has been a fear that a leakage current is increased when resin encapsulating is performed between wires or over parts of leads.
On the other hand, similarly to the semiconductor device, another resin-encapsulated semiconductor device is disclosed in Unexamined Japanese Patent Publication No. Hei. 5-129476. That is, this resin-encapsulated semiconductor device has a double-layer structure of encapsulating resin layers, one of which is an encapsulating resin layer for encapsulating the outside portion of the semiconductor package with an encapsulating material mixed with a radio wave absorbing material for shielding from electromagnetic waves, while the other is an encapsulating resin layer for encapsulating the inside portion with related-art insulating encapsulating resin. In this semiconductor device, resin-encapsulating using an encapsulating material mixed with radio wave absorber particles coated with resin or rubber whose melting point is not lower than the melting point of the encapsulating material is proposed as a measure against leakage among pins of lead frames or among wirings of a printed board. However, because of coating with an organic material such as resin or rubber in such a manner, there has been a problem that the hardness is so low that sufficient electric insulation properties are hardly kept under high mechanical shearing in a melt kneading process of the encapsulating material.
The invention was developed in consideration of such circumferences. An object of the invention is to provide a semiconductor device resin-encapsulated with an encapsulating material superior in electric insulation properties so as to have an electromagnetic wave shielding function, and an epoxy resin composition used for encapsulating a semiconductor in the semiconductor device.
In order to attain the foregoing object, an epoxy resin composition according to a first gist of the invention, as a material for forming a second encapsulating resin layer is to be formed on an outer circumference of a first encapsulating resin layer for encapsulating a semiconductor element, and the epoxy resin composition contains the following components (A) to (D):
(A) epoxy resin;
(B) phenolic resin;
(C) curing accelerator; and
(D) at least one of the following particles (d1) and (d2):
(d1) conductive particles whose surfaces are subjected to coating treatment with an insulating inorganic material; and
(d2) magnetic particles whose surfaces are subjected to coating treatment with an insulating inorganic material.
In addition, a semiconductor device according to a second gist of the invention comprises a semiconductor element; a first encapsulating resin layer for encapsulating the semiconductor element; and the second encapsulating resin layer being made of the aforementioned epoxy resin composition and being formed on the outer circumference of the first encapsulating resin layer.
That is, in order to obtain a resin-encapsulated semiconductor device superior in electromagnetic wave shielding function, the inventor et al. conducted a series of investigations chiefly into compounding materials of an epoxy resin composition which is used for the resin encapsulating and which is superior in electric insulation properties. As a result, the inventor et al. found that not only an electromagnetic wave shielding function but also electric insulation properties were improved conspicuously when a semiconductor element is resin-encapsulated with encapsulating resin layers in a double-layer structure, and special conjugated inorganic particles [component (D)] obtained by coating the surfaces of conductive particles or magnetic particles with an insulating inorganic material are used as a material for forming the second encapsulating resin layer of the double-layer structure disposed in the outside portion. Thus, the inventor et al. achieved the invention.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.